1. Field of the Invention
The present invention relates to a method of producing a solar cell module having a laminating step of sealing a photovoltaic device with a sealing member for protection of the photovoltaic device.
2. Related Background Art
There are various types of solar cell modules using crystalline silicon, polycrystalline silicon, microcrystalline silicon, amorphous silicon, compound semiconductor, or the like as a photovoltaic device. However, those photovoltaic devices, as they are, have no tolerance for usage under a harsh environment such as an outdoor usage. The reasons resides in that the photovoltaic device itself is liable to suffer from corrosion and easily broken by an external impact or the like.
Therefore, there is a need to protect the photovoltaic device by covering it with a sealing member. For the protection of the photovoltaic device, a laminating method of fastening the photovoltaic device between a surface member such as glass and a back surface member which have excellent weatherability, such as a fluororesin film through a sealing resin is most commonly adopted. Glass excels in weatherability and prevents passage of moisture, therefore being one of the best materials for a member covering the photovoltaic device, which is a semiconductor. Therefore, in most of the solar cell modules, glass is used for the surface member of a light receiving surface side.
On the other hand, advantages of a thin film solar cell such as being lightweight, impact resistant, and flexible cannot be exerted because glass covering brings about problems such as being 1) heavy, 2) inflexible, 3) weak against impact, and 4) high-cost.
Therefore, conventionally, a solar cell module making a full use of lightweight and flexible characteristics of the thin film solar cell by using a transparent fluoride polymer thin film such as a fluororesin film as the surface member is proposed.
Meanwhile, in order to produce such a solar cell module, an apparatus for laminating the photovoltaic devices, connected in series or in parallel, with a sealing member is used. Examples of such an apparatus include a laminating apparatus of so-called double vacuum chamber method having a chamber section composed of an upper chamber and a lower chamber parted by a diaphragm, and is disclosed in U.S. Pat. No. 6,149,757 (Japanese Patent Application Laid-Open No. H09-141743) entitled “Laminating apparatus”, Japanese Patent Application Laid-Open No. H10-214987 entitled “Laminator of solar cell module and lamination method”, U.S. Pat. No. 6,380,025 (Japanese Patent Application Laid-Open No. 2000-349309) entitled “Method of encapsulating a solar cell module”, or the like.
The laminating apparatuses disclosed in the above-mentioned documents have the upper chamber provided with the diaphragm freely expanding downward and the lower chamber provided with a heater board, and the upper chamber and the lower chamber can be freely opened or closed. The apparatuses are configured to depressurize the upper chamber and the lower chamber while mounting a body to be laminated onto the heater board provided in the lower chamber, heat the body to be laminated, and introduce an atmospheric air into the upper chamber, to thereby laminate the body to be laminated by pressing the body to be laminated between a top surface of the heater board and the diaphragm.
FIG. 4 is a view showing an example of a laminator manufactured according to a conventional double vacuum chamber method. The laminator includes a lower chamber 201, an upper chamber 202, a diaphragm 203, a mounting board 204, a heater 205, exhaust ports 206 and 207, an O-ring 208, and a body to be laminated 209.
A laminating method for a solar cell module using this type of apparatus is performed in accordance with the steps described below. First, the body to be laminated 209 is mounted on the mounting board 204 of the lower chamber 201, and the upper chamber 202 is mounted on the lower chamber 201. Next, the upper chamber 202 and the lower chamber 201 are both evacuated; the upper chamber 202 is set back to an atmospheric pressure while evacuating the lower chamber 201; and the body to be laminated 209 is contact-bonded to the diaphragm 203. Then, the body to be laminated 209 is heat-bonded with heat from the heater 205.
Further, a solar cell module can be produced using a single vacuum chamber method as well. The single vacuum chamber method is the same as the double vacuum chamber method except that an upper chamber is not provided and is disclosed in U.S. Pat. Nos. 6,007,650 B and 6,227,270 B (Japanese Patent Application Laid-Open No. H09-51114) entitled “Vacuum laminating apparatus”, U.S. Pat. No. 6,320,115 (Japanese Patent Application Laid-Open No. H09-36405) entitled “Solar cell module and a lamination method”, or the like. An example of the apparatus is shown in FIG. 5. The apparatus includes a mounting board 301, a diaphragm 302, a heater 303, an exhaust port communicating with the outside 304, an O-ring 305, and a body to be laminated 306.
A laminating method for a solar cell module using this apparatus is performed in accordance with the steps described below. First, the body to be laminated 306 is mounted on the mounting board 301, and the diaphragm 302 is stacked thereon. Next, the chamber is evacuated through the exhaust port 304 and the diaphragm 302 is caused to be sucked to the mounting board 301, thereby the body to be laminated 306 is contact-bonded to the diaphragm 302. The exhaust port 304 communicates a space, which is between the diaphragm 306 and the mounting board 301 sealed by the O-ring 305, with the outside. Then, the body to be laminated 306 is heat-bonded with heat from the heater 303.
In the laminating methods for the solar cell module, the body to be laminated is heated by electrifying the heater after contact-bonding the body to be laminated with the diaphragm. However, when manufacturing the solar cell modules, the mounting board is heated all the time in most cases. This will allow a prompt start of heating of the body to be laminated concomitantly with mounting thereof on the mounting board. In case of conducting lamination repeatedly, there is no need to cool the mounting board every time, which allows an increase of productivity with an enhanced throughput.
However, in a conventional laminating method for a solar cell module, when a body to be laminated is mounted on a heated mounting board, the body to be laminated and the mounting board contact each other directly, thereby rapidly raising the temperature of the body to be laminated and rapidly decomposing a crosslinking agent in a sealing member. Bubbles from gas generated hereby remain in the sealing member, causing a problem of so-called foaming phenomenon.
In particular, recently, lowering of the cost of a solar cell module is highly demanded. In such a flow, attempts of markedly thinner and simpler sealing configurations compared to those in existence are made. However, the thinner the sealing member, the faster the rise in the temperature of the body to be laminated, and easier for the foaming phenomenon to occur.
In addition, for lowering the cost of a photovoltaic device itself, thin film solar cells such as a thin film polycrystalline silicon solar cell, a thin film microcrystalline silicon solar cell, an amorphous silicon solar cell, and a thin film compound semiconductor solar cell have attracted attention. However, those solar cells also bring about a problem of a rapid temperature rise of the body to be laminated due to thickness reduction, similarly to the sealing member.
On the other hand, with the diversification of the solar cell modules, there are cases of simultaneously laminating a large number of modules with a much smaller size than that of the mounting board. In such a case, there was a problem in that the body to be laminated initially mounted on the mounting board was heated more than necessary, causing a variation in module quality.